Manufacture of non-woven fibrous material from a foamed furnish

ABSTRACT

Non-woven fibrous material is manufactured from a foamed fibre dispersion fed to a foraminous support and the invention resides in forming the foamed fibre dispersion by applying a vacuum to the underside of the support to recover a major part of the liquid from the dispersion on the support, delivering the recovered liquid to a mixer and mixing the recovered liquid in the mixer with fibres, a air, and a surface active agent to obtain a mixture thereof which is fed to a foaming device in which the foamed fibre dispersion is formed for feeding to the support.

United States Patent [191 Robertson Mar. 18, 1975 [5 MANUFACTURE orNON-WOVEN FIBROUS MATERIAL FROM A FOAMED FURNISH [75] Inventor: NeilGeorge Douglas Robertson,

Marlow, England {73] Assignee: Wiggins Teape Research &

Development Limited, London, England Filed: Apr. 6, 1973 Appl. No.:348,596

[30] Foreign Application Priority Data Apr. 7, 1972 United Kingdom16210/72 Mar. 30, 1973 United Kingdom 15344/73 [52] US. Cl 162/101,162/202, 162/289 [51] Int. Cl D2ld 3/00 [58] Field of Search 162/101,202, 289, 336, 162/343; 261/D1G. 26; 252/359 E; 425/4;

[56] References Cited UNITED STATES PATENTS Green et a1. 162/343 2/1970Roberts 162/152 2/1973 Gatward et a1. 162/101 Primary ExaminerS. LeonBashore Assistant Examiner--Peter Chin Attorney, Agent, or Firm-Burns,Doane, Swecker & Mathis [57] ABSTRACT Non-woven fibrous material ismanufactured from a foamed fibre dispersion fed to a foraminous supportand the invention resides in forming the foamed fibre dispersion byapplying a vacuum to the underside of the support to recover a majorpart of the liquid from the dispersion on the support, delivering therecovered liquid to a mixer and mixing the recovered liquid in the mixerwith fibres, a air, and a surface active agent to obtain a mixturethereof which is fed to a foaming device in which the foamed fibredispersion is formed for feeding to the support.

4 Claims, 3 Drawing Figures MANUFACTURE OF NON-WOVEN FIBROUS MATERIALFROM A FOAMED FURNISH BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to the manufacture of nonwoven fibrousmaterial, for example paper.

2. Description of the Prior Art It is known to manufacture paper andother nonwoven fibrous material by depositing a suspension of fibres ina liquid, usually water, onto a foraminous support, called the wire, ofa paper-making machine, which allows the liquid to drain through whileretaining most of the fibres in the form of a web in which the fibreslie intermeshed, all substantially in the plane of the web. Due to therandom nature of the process of deposition, and also because of thenatural tendency of most fibres to form flocs, or clumps, the web isusually not uniform but contains areas which are particularly thin orlight, or which are particularly thick or heavy. The degree ofuniformity, or the lack of uniformity, of the web, may be controlled tosome extent by the exercise of the machine operators skill and by thedesign of the machine. In particular, the formation of acceptablyuniform webs from fibres which have an excessive tendency to flocculate,or clump together, such as long synthetic fibres, or long, lightlybeaten cotton or wood fibres, or other long natural fibres from animal,vegetable or mineral sources, requires that the fibres be dispersed invery large volumes of liquid. The subsequent drainage of such largevolumes of liquid cannot be ac complished on conventional paper-makingmachines but requires costly modifications thereto. A less common knownmethod of manufacturing fibrous material is that in which fibres arefirst dispersed in a liquid medium of high viscosity, such as an aqueoussolution of sugar, or of natural gums, the dispersion then being drainedthrough the wire of a paper-making machine thereby to form a fibrous webon the wire.

This method has the advantage that when the dispersing action ceases,the fibres very quickly cease their motion in the liquid medium, andbecome immobile before they can become flocculated and clumped togetherto any appreciable extent. Thus, the fibres in such a liquid mediumremain well dispersed until the liquid medium is drained from thedispersion and the web formed. However, due to the always high viscosityof the liquid medium initial dispersion of fibres therein is difficult,and its drainage through the forming web and through the supporting wireis slow and difficult, so that this known method is not well suited tothe largescale continuous manufacture of fibrous material.

It has also been proposed to add a surface active agent to the waterconventionally used in the waterlaying of fibrous webs on a paper-makingmachine, and by agitation produce a foamed fibre dispersion having anair content of at least 65% by volume to assist in the formation of auniform fibrous web and, more especially, a uniform fibrous webcomprising fibres longer than those conventionally employed in thewater-laying manufacture of fibrous webs on a paper-making machine, i.e.fibres having a length in excess of about 3 Known methods of formingsuch a foamed fibre dispersion involve subjecting water containingsurface active agent to a vigorous shearing action, for example by theuse of apparatus comprising a casing for containing the water, and animpeller mounted within the casing for rotation relative thereto suchthat the water is subjected to a vigorous shearing action between bladesof the impeller and an inner surface of the casing. With the use of suchapparatus fibres can be added either to the water prior to foamingthereof or to foam already formed in the apparatus.

Known foamed fibre dispersion forming apparatus as described above,while being effective to form dispersions having required properties,has the disadvantage that it comprises relatively moving parts, i.e. theimpeller and the casing, and thus requires an input of power to providethe necessary movement. Further, the relative movement of the partsresults in wear in the apparatus.

SUMMARY It has now been discovered, firstly that fibrous material havinga higher degree of uniformity of fibre dispersion throughout thematerial than can be produced at the same weight consistency using onlywater as the dispersion medium, can be manufactured using a foamedliquid medium having an air content above a lower limit less thansecondly that there is an air content level for the foamed liquid mediumabove which although the dispersion of fibres in the foamed liquidmedium is more uniform than can be obtained at the same weightconsistency using only water as the dispersion medium, nevertheless thefibres in the foamed liquid medium have a tendency to agglomerate; andthirdly that the size distribution of the bubbles in the foamed liquidmedium is of considerable importance.

It has also been discovered that not all foamed liquid media comprisingair bubbles dispersed in a liquid containing a surface active agent areuseful for dispersing fibres, and in fact that certain foamed liquidmedia can be used to produce agglomeration of fibres (and particles)rather than dispersion thereof, albeit that the overall fibre dispersionmay be better than could be obtained at the same weight consistencyusing water only as the dispersion medium.

It has been further discovered that an important parameter in relationto the dispersion/agglomeration properties ofa foamed liquid medium ofthe kind under consideration is the volume percentage of air therein,and that the possible volume percentage of air range (ie. 0% to about999%) can be divided into three subranges two of which, namely up toabout 55% and over about can be used to effect agglomeration of fibresand/or particles, and the other, namely from about 55% to about 75%, canbe used to effect substan tially uniform dispersion of generallydiscrete fibres.

The volume percentage of air required to effect the most uniformdispersion of any particular fibres and/or particles is generallydependent upon the shape, size, physical properties and concentration ofthe fibres and- /or particles. The relationship between the size of thefibres and/or particles and the arithmetic mean diameter of the airbubbles is also relevant in determining the most uniform dispersion ofany particular fibres and/or particles.

It has been ascertained that at all volume percentages of air, fibresnormally occupy only the liquid between the air bubbles; that is thatfibres do not penetrate the air bubbles. Thus, factors determiningwhether a particular foamed liquid medium will effect dispersion oragglomeration of fibres apart from the volume percentage or air thereinare the number, shape and size of the air bubbles in the medium.

When the foamed liquid medium contains a volume percentage of air ofbetween about 55 and 75%, the fibres are dispersed substantially,uniformly throughout the foamed liquid medium.

When the volume percentage of air in a foamed liquid medium is less thanabout 55%, the air is contained in a relatively few relatively widediameter range bubbles which divide the medium into pockets of liquid inwhich the fibres collect, and as the viscosity of the liquid (normallywater) is relatively low, the fibres are free to move and thusagglomerate within the liquid pockets.

When the volume percentage of air in a foamed liquid medium is greaterthan about 75% and the bubbles have a substantially uniform sizedistribution, the packing density of the bubbles is so high that thebubbles are deformed from their normally spherical shape intopolyhedrally shaped bubbles. In a medium containing such bubbles,surface tension effects result in forces in the planes of theinter-bubble lamellae, the forces being directed towards the line ofintersection of the lamellae and into the points of intersection of thelines of intersection of the lamellae. These forces move fibres into thelines of intersection of the lamellae and the fibres become aligned inbundles in these lines.

However, although when using a foamed liquid medium having a volumepercentage of air above 75% therein there is some degree of fibreagglomeration, nevertheless the overall fibre dispersion in a webproduced using such a foam can be better than can be obtained at thesame fibre weight consistency using only water as the dispersion medium.

Work has shown that as the volume percentage of air in a foamed liquidmedium increases, firstly the number of bubbles per unit volume of themedium increase; secondly the arithmetic mean diameter ofthe bubblesdecreases; and thirdly the range of bubble diameters decreases. Theinherent desirable viscosity properties of the foamed liquid mediumproduced in accordance with the present invention derive from not onlythe number of bubbles therein per unit volume, but also from thesubstantially uniform size of the bubbles.

The effect on the viscosity of the medium of the bubble sizedistribution is thought to result from the fact that the volumepercentage of air required for close packing of the bubbles is less ifthe bubbles have a substantially uniform size distribution.

The chemical nature of the surface active agent used is not criticalprovided that it is able to produce a foamed liquid medium having thespecified properties. The surface active agent may be anionic, cationic,or nonionic, and it has been found that proprietary surface activeagents such as that sold under the name ACE" liquid, this being ananionic substance, by Industrial Soaps Ltd., that sold as TEXOFOR(Registered Trade Mark) FN 15, a non-ionic substance by Glover ChemicalsLtd., and that sold as AMINE I Fbl9, a cationic substance, by Float-OreLtd. are all suitable. Other surface active agents that have been usedare oxtylphenoxypolyethoxy ethanol, and commercial grade dodecyl benzenesulfonate.

The arithmetic mean diameter of the bubbles in a foamed liquid mediumcan be determined by plunging a microscope slide cooled to about 70Cinto the medium, and then removing the slide with a sample of the mediumfrozen thereto and placing the slide into a freezing stage of amicroscope. Photomicrographs at say lOO'X magnification can then betaken and the arithmetic mean diameter of the visible bubbles thendetermined therefrom. This method has the advantage that a sample of themedium is taken from within the medium mass, and it is no only the outerlayer of bubbles that is examined.

It is a main object of the present invention to provide such a method ofand apparatus for manufacturing non-woven fibrous material from a foamedfibre dispersion, which method and apparatus permits liquid, generallyin a foamed condition, recovered by vacuum boxes to be recirculated to amixer in which a gas/water/fibre/surface active agent dispersion isformed preparatory to being converted into a foamed fibre dispersion,having required properties, thereby reducing wastage of surface activeagent, reducing operating and maintenance costs, and substantiallyreducing the need for effluent treatment.

According to one aspect of the invention there is provided a method ofmanufacturing non-woven fibrous material, for example paper, by feedingto a foraminous support from a foaming device a foamed fibre dispersionformed by the foaming device, said method including the steps of formingthe foamed fibrous dispersion which is fed to the support by recoveringa major part of the foamed water from foamed fibre dispersion on thesupport by connecting the input side of a vacuumcreating device to theunderside of the support and the output side to a mixer, introducingfibres into the mixer, together with recovered foamed water, a air andsurface active agent, and following mixing thereof in the mixer feedingthe air/water/fibre/surface active agent mixture to the foaming device.

According to another aspect of the invention there is provided in amachine for manufacturing non-woven fibrous material, which machineincludes a foraminous support on which the material is formed, apparatuscomprising a closed foaming device arranged to form a foamed fibredispersion and to feed the dispersion for deposition on the support; amixer; vacuum-creating means to drain liquid from foamed water fromfoamed fibre dispersion on the support, the negative pressure side ofthe vacuum-creating means being connected to the underside of thesupport and the positive pressure side being connected to the mixer;means operable to deliver to the mixer foamed water drained from foamedfibre dispersion on the support; and means connecting the mixer with thefoaming device to deliver thereto a water/fibre/air/surface active agentmixture formed in the mixer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates diagrammaticallyapparatus for carrying into effect the method according to theinvention,

FIG. 2 illustrates diagrammatically, in plan, one form of apparatus forforming a foamed fibre dispersion, and

.FIG. 3 is a section diagrammatically illustrating a part of theapparatus of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawings, thereference 1 indicates a foraminous support, being the wire of aFourdrinier paper-making machine, on which there is deposited from ahead box 2 a foamed fibre dispersion, not shown, from which a non-wovenfibrous material is formed by draining water, generally in a foamedcondition, from the dispersion through the foraminous support 1.Draining is effected, in known manner by vacuum-creating means 3 and 4the negative pressure sides of which are connected to the underside ofthe support 1. As can be seen from FIG. 1, the vacuum-creating means 3and 4 are spaced apart along the support and between the means 3 and 4the support 1 passes over what are known as table rolls 5. Somedrainage, about 20%, takes place as the dispersion passes over the rolls5 and the water so drained falls into a wire pit 6 from which itoverflows over a weir 7 into a hog pit 8 in which it is slushed by anagitator 9 and from which it is pumped by a pump 10 into a broke tank11. The vacuum-creating means are associated respectively with what areusually termed wet vacuum boxes 12 and dry vacuum boxes 13.

The positive pressure sides of the vacuum-creating means arerespectively connected by pipes 14 and 15 with a pipe 16 in whichdrained foamed water containing surface active agent meets and becomesinfused with a mixture of air/water/fibres/surface active agent fed tothe pipe 16 by a pump 17 at a pressure of about 25 to 30 pounds persquare inch. The pipe 16 is connected with an in-line mixer 18, of anysuitable kind which effects a coarse mixing of the mixture to provide afairly homogeneous mixture which passes from the mixer through an inletpipe 19 to an in-line foaming device 20 in which a foamed fibredispersion, having desired properties as referred to above, is formedfor delivery through an outlet pipe 21 to the head box 2. The foamingdevice may be of any suitable closed kind, but is preferably of the kinddescribed below with reference to FIG. 2 because this does not utiliseany mechanical moving parts, it is not open to atmosphere, and it ispossible to admit metered quantities of air and surface active agent toa water/fibre dispersion as the latter approaches the mixer.

As is usual in the manufacture of non-woven fibrous material, the fibreis first beaten with water in a conventional beater 22, such as aHollander beater, to form stock having a consistency of about 4% byweight based on bone dry fibre. The stock is pumped by a pump 23 tochests 24 where it is held to provide bulk storage for the apparatus,the fibre being kept substantially uniformly in suspension byconventional agitators 25. From the chests 24 the stock is pumped alonga line 26 by a pump 27 to a refiner 28 from which the stock passes to athickener 29. The thickener serves to dewater the stock so that itleaves the thickener at a consistency which is usually between 20% and30% by weight based on bone dry fibre, but should be sufficiently highto minimise the input of fresh water into the apparatus while achievingthe required dryness for the web that is removed from the foraminoussupport 1 prior to drying. Water extracted from the stock in thethickener 29 is removed through a drain pipe 30 and may either go todrain or be re-directed for reuse in the beater 22. The thickened stockis delivered to a pulper 31 in which it is mixed by conventionalagitating means 32 with water which is stored in a tank 33 whichreceives drained foamed water from pipe 14 through a valve 34, and withbroke pumped to tank 33 from the broke tank 11 by a pump 35, passing ifdesired through a broke deflaker 36.

Surface active agent may, if desired, be added to the water in tank 33but it is preferred to admit both air and surface active agent to thewater/fibre dispersion as it flows through a pipe 37 to the pipe 16. Thepump 17 is included in pipe 37 and the air and surface active agent aredelivered into pipe 37, preferably on the output side of pump 17,through metering devices 38, 39 respectively. A deflaker 40 which servesto disperse clumps of fibres is also included in pipe '37.

The preferred kind of foaming device 20 mentioned above comprises aplurality of foam-forming pipes 41, which may consist of flexible tubes,each of which has at least one internal region of constrictedcross-section formed by a tubular insert 42 which may be circular or ofother desired cross-section. An inlet manifold, formed by a housing 43,and an outlet manifold, formed by a housing 44, are connected one to theother by the foam-forming pipes 41. The inlet manifold is connected tothe inlet pipe 19 by a flange 45 and the outlet manifold is connected tothe outlet pipe 21 by a flange 46. Each foam-forming pipe 41 extendslaterally from a housing and is coiled, as at 47, between the endsthereof connected respectively to the inlet and the outlet housing. In apreferred embodiment the housings 43, 44 are circular and thefoam-forming pipes extend radially therefrom.

Each end of each of the foam-forming pipes is connected to a housing 43,44 through a manually operable valve 48 connected to a stub pipe 49extending laterally from the housing. The tubular inserts 42 areconnected to the valves 48 and the foam-forming pipes 41 are fitted overthe inserts 42 as illustrated in FIG. 3.

One end 50 of the inlet housing 43 is open to comm unicate with theinlet pipe 19 and the end ofthe housing opposite said open end is closedby a plug 51, FIG. 3, having a conical configuration 52 extending intothe housing to prevent the formation of air pockets in the inlet housing43.

There may be forty-eight foam-forming pipes 41 arranged in four ranks orbanks each of twelve pipes and the housings 43, 44 are preferablyindependently supported so that little or no vibration is transmittedbetween the inlet and outlet manifolds. Generally before using thefoam-forming apparatus to make any particular kind of product the numberof foam-forming pipes to be used is selected by manipulation of thevalves 48. If desired, the number of foam-forming pipes 41 in use can bechanged during operation of the apparatus by manipulation of the valves48.

When the foam-forming apparatus is in operation a mixture of air, waterand fibre, and surface active agent fed to the manifold 41 issubstantially equally divided into each foam-forming pipe and thetubular inserts 42 set up turbulence in the mixture which effectsfoaming and dispersion of the fibres, to provide a foamed fibredispersion having desired properties as referred to above.

From the foregoing description it will be understood that recovereddrained liquid is continuously recycled through a loop formed by thepipes 14, 15, 16 mixer 18, pipe 19, and foaming device 20, thus reducingthe quantity of make-up surface active agent required, and that by usingthe described preferred form of foaming device it is possible, bymetering air and surface active agent into the approach flow system, toprovide control over the air content and thus the viscosity of the foam.

I claim:

1. A process for manufacturing a non-woven fibrous material from afoamed fiber dispersion fed to a foraminous support from a foamingdevice wherein the amount of surface active agent required is reduced,the process comprising:

establishing an air/water/fibers/surface active agent mixture providedby a mixer; delivering said mixture to a closed foaming device andeffecting foaming thereof by the creation of turbulence without the useof moving mechanical means to establish said foamed fiber dispersion;

feeding said foamed fiber dispersion to said foraminous support;

recovering, by vacuum draining through vacuum box means, a major part ofthe liquid, generally in a foamed condition, from said foamed fiberdispersion on said foraminous support;

recirculating said liquid so recovered generally in a foamed conditiondirectly from said vacuum box means to said mixer;

introducing into said mixer, together with said recir culated liquid,fibers, water and metered quantities of air and make-up surface activeagent;

directing the contents of said mixer to said foaming device; and

repeating said feeding, recovering, recirculating, in-

troducing and directing steps.

2. The method according to claim 1 including the step of dispersingclumps of fibers following introduction of metered quantities of air andsurface active agent and prior to passage to the mixer.

3. A closed circuit system for manufacturing nonwoven fibrous materialfrom a foamed fiber dispersion wherein the amount of surface activeagent required is reduced, the system comprising:

a mixer for establishing an air/water/fibers/surface active agentmixture;

a closed foaming device, downstream of said mixer,

for effecting foaming of said mixture by the creation of turbulencewithout the use of moving m echanical means;

pipe means for deliverying said mixture from said mixer to said closedfoaming device;

feeding means for feeding said foamed fiber dispersion effected by saidclosed foaming device to a foraminous support on which said non-wovenfibrous material is formed;

vacuum drain means, including vacuum box means, for recovering a majorpart of the liquid, generally in a foamed condition, from said foamedfiber dispersion on said foraminous support;

a pulper connected by pulp delivery pipe means to said mixer;

pump means operable to recycle said liquid so recovered generally in afoamed condition directly from said vacuum box means through said pulpdelivery pipe means to said mixer; and metering means operable tointroduce into said pulp delivery pipe means upstream of said mixermetered quantities of air and make-up surface active agent.

4. The system according to claim 3 including a deflaker in said pulpdelivery pipe means, downstream of said metering means and upstream ofsaid mixer, for effecting dispersion of fiber clumps passing throughsaid pulp delivery pipe means.

1. A PROCESS FOR MANUFACTURING A NON-WOVEN FIBROUS MATERIAL FROM AFOAMED FIBER DISPERSION FED TO A FORAMINOUS SUPPORT FROM A FOAMINGDEVICE WHEREIN THE AMOUNT OF SURFACE ACTIVE AGENT REQUIRED IS REDUCED,THE PROCESS COMPRISING: ESTABLISHING AN AIR/WATER/FIBERS/SURFACE ACTIVEAGENT MIXTURE PROVIDED BY A MIXER; DELIVERING SAID MIXTURE TO A CLOSEDFOAMING DEVICE AND EFFECTING FOAMING THEREOF BY THE CREATION OFTURBULENCE WITHOUT THE USE OF MOVING MECHANICAL MEANS TO ESTABLISH SAIDFOAMED FIBER DISPERSION; FEEDING SAID FOAMED FIBER DISPERSION TO SAIDFORAMINOUS SUPPORT; RECOVERING, BY VACUUM DRAINING THROUGH VACUUM BOXMEANS, A MAJOR PART OF THE LIQUID, GENERALLY IN A FOAMED CONDITION, FROMSAID FOAMED FIBER DISPERSION ON SAID FORAMINOUS SUPPORT; RECIRCULATINGSAID LIQUID SO RECOVERED GENERALLY IN A FOAMED CONDITION DIRECTLY FROMSAID VACUUM BOX MEANS TO SAID MIXER;
 2. The method according to claim 1including the step of dispersing clumps of fibers following introductionof metered quantities of air and surface active agent and prior topassage to the mixer.
 3. A closed circuit system for manufacturingnon-woven fibrous material from a foamed fiber dispersion wherein theamount of surface active agent required is reduced, the systemcomprising: a mixer for establishing an air/water/fibers/surface activeagent mixture; a closed foaming device, downstream of said mixer, foreffecting foaming of said mixture by the creation of turbulence withoutthe use of moving mechanical means; pipe means for deliverying saidmixture from said mixer to said closed foaming device; feeding means forfeeding said foamed fiber dispersion effected by said closed foamingdevice to a foraminous support on which said non-woven fibrous materialis formed; vacuum drain means, including vacuum box means, forrecovering a major part of the liquid, generally in a foamed condition,from said foamed fiber dispersion on said foraminous sUpport; a pulperconnected by pulp delivery pipe means to said mixer; pump means operableto recycle said liquid so recovered generally in a foamed conditiondirectly from said vacuum box means through said pulp delivery pipemeans to said mixer; and metering means operable to introduce into saidpulp delivery pipe means upstream of said mixer metered quantities ofair and make-up surface active agent.
 4. The system according to claim 3including a deflaker in said pulp delivery pipe means, downstream ofsaid metering means and upstream of said mixer, for effecting dispersionof fiber clumps passing through said pulp delivery pipe means.